Photographic elements are coated on a wide variety of support materials, such as plastic resins, paper and glass. Plastics are used as the support when a combination of transparency, strength, dimensional stability and light weight is needed. Paper is used when the physical properties are not too demanding, cost is a major factor or an opaque base is needed. Glass has the advantages of excellent dimensional stability and extreme flatness, but is disadvantageous in that it is expensive, heavy and brittle. Photographic glass supports typically range in thickness from about 1 to 10 millimeters and are graded by flatness. Those with the lowest degree of flatness are used in such applications as photomicrography and graphic arts, those with an intermediate degree of flatness are used in such applications as photofabrication, stereoplotters and aerial photography, and those with the highest degree of flatness are used in such applications as high-precision stereoplotters, ballistic and aerotriangulation camera systems and special scientific investigations.
The coating of glass plates with photographic layers is a very demanding art since the layers must be extremely thin, highly uniform in thickness, and completely free from defects. One technique for coating such layers based on wicking action using an arcuate surface is described in U.S. Pat. No. 4,033,290 (Dude). There are many difficulties in coating glass substrates, including the likelihood of "skips" that result in uncoated areas, the difficulty in coating extremely thin layers, and the presence of streaks and contaminants such as dust. There is a continuing need to reduce or eliminate these problems.
One attempt at this is described in U.S. Pat. No. 5,254,447 (Meyer et al) in which various layers are applied to glass plates by lamination techniques. Such techniques solve certain problems such as protection of the photosensitive layers, and other features described in the noted patent. Moreover, these techniques allow for the production of multilayer plates that were difficult to prepare using previously known coating techniques.
However, lamination of various layers to provide photographic glass plates has a number of disadvantages. Dirt entrapped between laminated layers can become prominent in the resulting element causing undesirable non-uniformities, sometimes called "tentpoles". In certain elements, protective overcoats are desired, but when matting agents are included in such overcoat layers, they cannot protrude because this layer rests on a film support prior to the lamination process. This renders the matting agent ineffective. In order to be effective, it is necessary that the matting agent protrude from the overcoat surface to provide excellent vacuum drawdown and reduced tackiness. Moreover, lubricants cannot readily be put into the protective overcoat layers using the prior art process because the lubricants decrease adhesion of the layers to the polymer films required in lamination procedures.
It would be desirable to provide photographic glass plates that contain antihalation layers beneath the photographic layer, over which is a protective overcoat that can contain a matting agent or lubricant. Such elements cannot be readily prepared by lamination techniques.